In the Song of Deborah’s list of groups that went to war, the phrase “from Ephraim, their root in/among Amalek” (Judg 5:14a) has not been adequately explained. To better understand this line and the odd relationship it seems to recall, I investigate the crucial lexeme “root” שרש (*šrš) in biblical and extrabiblical sources. The analysis reveals that a “root” metaphorically refers to a man’s current or future “patrilineage,” that is, his line of male ancestors and offspring. In the Song of Deborah, the “root” of Ephraim therefore refers to one or many of its high-ranking patrilineal lines. Abdon ben Hillel in Judg 12:13–15 supports this conception, as he is, on the one hand, crucially buried at a location defined by both Ephraim and Amalek and, on the other, is portrayed as a prolific progenitor of male sons. In applying this definition of “root” to the internal logic of the Song of Deborah, I conclude that the fighting force from Ephraim was a body of high-ranking lineage-based leadership that mustered Amalekites (and Benjaminites) to war in the Jezreel valley. Alongside Ephraim’s leader(s), Amalek too fought for the allied “people of YHWH” (Judg 5:13).